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单选题
A centrifugal impeller consists of a number of vanes curving （） from the direction of rotation.
A
backwards
B
forwards
C
upward
D
downwards
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更多 “单选题A centrifugal impeller consists of a number of vanes curving （） from the direction of rotation.A backwardsB forwardsC upwardD downwards” 相关考题
考题
第二组Displacement pumps are those where the volume of the pump chamber is alternately increased to draw the liquid in from the suction pipe and then decreased to force the liquid out into the delivery pipe. Centrifugal pumps are those wherein an impeller rotating at high speed throws the liquid by centrifugal force from the center to the periphery of the impeller where the liquid is discharged through the delivery outlet.Gear pump consists of two or more meshing gears (spur, single or double helical teeth) enclosed m a close-fitted housing. These are used extensively for pumping fuel oil, lubricating oil and hydraulic oil. When gears are unmeshed on the inlet side, a pressure drop occurs that helps the atmospheric pressure acting on the surface of the oil in the reservoir to force it up the pipe to fill the void, the oil is then transferred around the periphery of the pump housing. As the gear teeth mesh again on the outlet side, they form. a seal that prevents oil from backing up to the inlet, the oil in the void is then be forced out into the discharge line.All vane pumps have a rotor driven within a ring (cam ring) by a drive shaft coupled to a prime mover. A cylindrical rotor with sliding vanes, generally in radial slots, rotates within the ring. The center of the rotor is offset from the center of the ring. In a simple vane pump, as the rotor turns, the vanes are forced outward against the inner surface of the cam ring by centrifugal force. This outward radial movement of the vanes and turning of the rotor causes the chamber between the vanes to increase as the vanes pass further away from the inlet port. This increase in volume results in a lowering of pressure until the atmospheric pressure is sufficient to force oil from the reservoir into the inlet chamber. Oil from the inlet is swept away by the vanes toward the outlet port through a decreasing series of chambers until it is forced through the outlet port. A vane pump of balanced design has an elliptical cam ring so that two pumping chambers are formed. This pump is in hydraulically balance, since the two intake and two outlet ports are diametrically opposed to each other. Therefore the side loads exerted on the rotor cancel out, thereby increasing bearing lift and permitting high operating pressure.According to the last sentence of paragraph 1, from where the liquid is discharged through the delivery outlet?A.from the eye of the impellerB.from passage of impellerC.from the periphery of the impellerD.from the impeller
考题
It is possible to mount a double suction centrifugal pump impeller with the vanes facing in the wrong direction. This would cause the pump ______.A.head capacity to improveB.discharge to be reversedC.efficiency to decreaseD.slippage to decrease
考题
A centrifugal pump may fail to deliver water when first started if the ______.A.water seal pipe is pluggedB.pump is not primedC.seal ring is properly locatedD.impeller is flooded
考题
What causes cavitation in a centrifugal pump ________．A.Vapor pockets in the flow streamB.Rough impeller surfacesC.Worn wearing ringsD.Heavy fluid in the flow stream
考题
单选题Which of the following statements is correct with regards to the operation of a centrifugal cargo pump?（）A
Oil is discharged from the impeller through the outletB
Gravity causes the oil to flow toward the dischargeC
The self-priming feature of the centrifugal pump enables it to draw its own suction as it startsD
The discharge capacity varies directly with the speed of the impeller
考题
单选题In a turbocharger, inlet air velocity is increased in the（）.A
inlet nozzle ringB
stationary diffuser passagesC
compressor outlet voluteD
rotating impeller vanes
考题
单选题A variable displacement system of hydraulic drives consists of （）.A
a variable displacement axial piston pumpB
a constant displacement axial piston pumpC
a reciprocating piston pumpD
a centrifugal pump
考题
单选题With reference to a rotary vane steering gear system, which one of the following statements is true?（）A
The three moving vanes and the three fixed vanes form three pressure chambersB
The three moving vanes and the three fixed vanes form six pressure chambersC
The three moving vanes and the three fixed vanes form nine pressure chambersD
The three moving vanes and the three fixed vanes form twelve pressure chambers
考题
单选题A double suction centrifugal pump impeller has been installed in the reverse direction, and will （）.A
have a greater head capacityB
operate with increased impeller efficiencyC
discharge through the suction side of the pump casingD
require more power to run the shaft
考题
单选题A multistage centrifugal pump can be BEST described as having （）.A
two or more impellers housed together in one casing and mounted on a single shaftB
a single stepped impeller mounted in a progressively staged casingC
a large radial clearance between the impeller and casing to prevent overheating due toD
an increase in the discharge velocity of the liquid with a corresponding decrease in pressure through the stages
考题
单选题Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.A
cavitationB
electrolysisC
abrasionD
corrosion
考题
单选题Increasing the speed of a centrifugal pump will result in an increase in its capacity Another means of increasing the capacity of a centrifugal pump is to increase the （）.A
diameter of the discharge piping, with all other factors remaining the sameB
diameter of the suction piping, with all other factors remaining the sameC
width of the impeller onlyD
diameter of the impeller
考题
单选题Increasing the speed of a centrifugal pump will result in an increase in its capacity in its capacityAnother means of increasing the capacity pump is to increase the（）A
diameter of the discharge piping, with all other factors remaining the sameB
diameter of the suction piping, with all other factors remaining the sameC
width of the impeller onlyD
diameter of the impeller
考题
单选题One of the main functions of wearing rings, as used in a centrifugal pump, is to （）.A
maintain radial alignment between the pump impeller and casingB
absorb all impeller shaft end thrustC
prevent water leakage to the atmosphereD
prevent wear of the pump casing and/or impeller
考题
单选题For optimum results, centrifugal purification of heavy fuel oil should be accomplished with the fuel at the lowest practicable（）A
throughputB
additive percentC
cetane numberD
TBN number
考题
单选题Attempts are made to eliminate axial thrust in centrifugal pump by （）.A
providing the impeller with balancing holesB
the use of symmetrical impellerC
neither A nor BD
either A or B
考题
单选题To absorb the wear resulting from impeller rotation and abrasives in the liquid, a centrifugal pump is usually fitted with （）.A
lantern ringsB
bearingsC
easing volutesD
wearing rings
考题
单选题It is possible to mount a double suction centrifugal pump impeller with the vanes facing in the wrong directionThis would cause the pump （）.A
head capacity to improveB
discharge to be reversedC
efficiency to decreaseD
slippage to decrease
考题
单选题Which of the listed statements is correct concerning the starting of centrifugal pumps?（）A
They should always be started with the discharge valve closedB
They should always be started with the discharge valve openedC
A priming pump is always required to flood the impeller suctionD
They should always be started with the sealing line valves closed
考题
单选题The basic function of the centrifugal pump impeller is to （）.A
directly increase the pressure of the liquid being pumpedB
directly increase the velocity of the liquid being pumpedC
convert the potential energy of the liquid to kinetic energyD
separate air from the liquid being pumped
考题
单选题A centrifugal pump produces the required pressure energy by means of a rotating （） provided with vanes.A
propellerB
impellerC
circumferenceD
screw
考题
单选题To maintain design discharge pressure from a centrifugal pump, the design clearance must be maintained between the （）.A
shaft and impellerB
motor and pump shaftC
casing and impeller wearing ringsD
lantern ring and impeller
考题
单选题Which features of a centrifugal pump reduce the need for renewing worn impellers and pump casings?（）A
Close radial clearance between impeller hub and casingB
Low rotational speed of impellerC
Removable end plateD
Replaceable impeller and casing wearing rings
考题
单选题The discharge head of a centrifugal pump will vary directly with the （）.A
change in impeller diameterB
square of the impeller diameterC
cube of the impeller diameterD
impeller efficiency for large changes in the size of the impeller
考题
单选题The discharge rate or capacity of a centrifugal pump will vary directly as the （）.A
change in the impeller diameterB
square of the impeller radiusC
cube of the impeller diameterD
impeller efficiency for large changes in its size
考题
单选题Centrifugal pumps, however, can be designed with a number of impellers （） to attain a large amount of liquid.A
in seriesB
in parallelC
assembledD
together
考题
单选题A centrifugal pump vibrates excessively during operationUpon disassembling the pump it is found that the impeller is out of balanceWithout an available spare, you should （）.A
drill holes through the heavy side of the impeller until it balancesB
weld counterweights to the light side of the impellerC
remove metal from the heavy side by machining in a latheD
acid wash and serape the heavy side until it balances
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